First Things You should know about UNIX
What is Unix ?
Unix is a Operating Environment. It can also be called as a Operating System. It's Origin is the "Unix system" developed by AT&T Bell labs.
Unix is a powerful Operating system which is more than 40 years since it was developed. It was developed before the advent of DOS and Windows operating system.
The Present day Unix system has many contributions made by IT industry and the student community worldwide. The open source movement is mainly due to Unix.
Give us a history on how Unix was developed ?
Unix was developed by Ken Thompson and Dennis Ritchie. In 1965, Bell Telephone Labs, General Electric, MIT (Project Mac) worked on MULTICS project. It also had a team of AT&T Engineers. The Project didn't materialize giving the intended results. This made AT&T back out of this project in 1969 and it resulted in Dennis and Thompson design and develop a system having it's own file system, utilities and command line interpreter. This however wasn't machine independent system and wasn't capable to run on different hardware.
Dennis who is the founder of C language rewrote this system in C language in 1973. This resulted in the Unix system become portable on different hardware. The different versions of this system was known to be
Editions, Systems, Systems III, Systems V Release 3.0, Systems V Release 3.2. The Final version was called as Unix System.
What does Unix Translate to ?
According to Dennis Ritchie in his 1974 CACM's ( Communications of the ACM) paper, UNIX ( All - Caps) meant "The Unix-Time Sharing System". Dennis Ritchie believed that it should be used in Small caps letter as "Unix" since it doesn't have any Acronym. Hence the right usage of the word should be "Unix" and not "UNIX".
Tell us more on what happened to AT&T and it's Unix system?
AT&T had plans to sell it's Systems V Release 3.2 commercially. This idea didn't get approval from the U.S government and this made AT&T distribute the software to Academic and research institutes. This resulted in the birth of BSD Unix.
BSD Unix
BSD Unix is Berkeley Software Distribution developed by "The University of California, Berkeley (UCB). They developed this system from the System V Release 3.2 version developed by AT&T. The BSD gathered worldwide attention and attracted universities and the students.
Further developments resulted in Berkeley rewrite their BSD Unix in their way. This resulted in developments of standard vi editor, c shell, TCP/IP, better file system, mail features and linking of files (symbolic links).
BSD Unix is the foundation of Solaris. Sun Micro systems used BSD as a foundation for the development of their own UNIX ( Sun OS). Sun Micro systems has now been acquired by Oracle and the Sun OS is called as "Oracle Solaris"
BSD Unix is the foundation of Solaris. Sun Micro systems used BSD as a foundation for the development of their own UNIX ( Sun OS). Sun Micro systems has now been acquired by Oracle and the Sun OS is called as "Oracle Solaris"
What are the Main Unix Flavors of BSD Unix ?
FreeBSD, NetBSD and OpenBSD.
What is System V Release 4 ( SVR4) ?
As different vendors created their own version of Unix, BSD release had incompatibilities and differed very much from the AT&T version. Hence AT&T reworked on the BSD product, System V 3.2, Sun OS and Microsoft's Unix version namely XENIX. They made the final version called as the System V Release 4 SVR4.
What happened later with AT&T after System V Release 4 (SVR4) ?
AT&T sold Unix to Novell. Novell then sold the rights to X/OPEN. X/Open merged with The Open Group.
Name the Different Flavors of Unix ?
Solaris by Oracle Solaris, AIX by IBM, HP-UX by Hewlett Packard, Tru64 UNIX (Discontinued) by Digital Equipment Corporation and lastly owned by HP, Linux by Red Hat, SUSE by Novell, CentOS, Fedora, Ubuntu, Debian.
POSIX and SINGLE UNIX SPECIFICATION.
These are two different Standard bodies in the Unix world. During the earlier years of development of Unix, it wasn't completely portable and this affected the development of applications that can be easily ported on various flavors of Unix and their hardware.
AT&T had their own standard mechanism called as System V interface definition. The X/Open ( The open Group) had their own. There was a standard called as POSIX ( Portable Operating System Interface for Computing Environments) developed by IEEE ( Institute of Electrical and Electronics Engineers). POSIX standards were based on Unix and they had two versions called POSIX.1 and POSIX.2.
Later, The Open Group and IEEE worked together to bring a common standard by unifying the X/Open and POSIX. This is known as "The Single UNIX specification". It was later approved by ISO ( International Organisation of Standardization). Today UNIX is owned by the The Open Group and most of the UNIX flavors are POSIX compliant.
Open Source and Free Software Foundation
Open source and free software foundation are almost identical except that fact that "Free Software" doesn't really mean that the software can be purchased free of cost. In most cases, the Free software is indeed free of cost, but only in few cases, you may be charged a fee for support or Royality
Both Open source and free software foundation preaches the usage of software freely, modify the source code and share the software to any number of people freely.
The free software comes with a GNU pronounced "guh-noo" ( GNU Not Unix !) license. Linux is one such Unix flavor which comes with a GNU license.
What is Linux ?
Linux is a Kernel. It's inappropriate to term it as a "Operating system". Linux was developed by Linus Torvalds, a student of the Helsinki University.
Linux is a Kernel because most of the applications in Linux are due to the outcome of GNU project. Hence if Linux has to be known as a operating system, it should be called as GNU/Linux.
What are the different GNU/Linux flavors ?
Red Hat, Calder, SuSE Linux, Debian, Mandrake, Fedora. There are Ubuntu and CentOS too.
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